Alternator Problem

How do you know if it’s your alternator?

Alternator Problem

A couple of weeks ago, I posted on how to determine if you have a dead battery.  Well, what if your battery keeps dying and your getting tired of jump starting it?  You could be having a problem with your alternator.  The function of the alternator is to charge the battery while the engine is running.  If this fails, your car relies purely on the power of the battery which drains it quickly.  There are two easy steps to determine if your alternator has failed.

Battery Light

The first thing you want to check is the battery MIL.  Check your dash lights to see if your battery light is on while the engine is running, it should look similar to the picture on the right.  If this light is on, that’s an indicator that your battery has a low charge.  Don’t let this determine your final diagnosis, I still recommend performing the following test to be absolutely sure it’s the alternator.

Perform a Voltage Test

You could pay somebody to test your alternator if you’d like but why not do it yourself when it can only take a couple of minutes.

To perform this test, you will need a basic multimeter that can read DC volts.  A lot of multimeters can read both AC and DC so make sure that yours is switched to DC.

  1. With the engine off, touch the red, positive lead of the multimeter to the positive terminal of the battery and the black, negative lead of the multimeter to the negative terminal of the battery.  With the engine off, you should be getting approximately 12.1 – 12.8 volts.
  2. While still holding the leads on the battery terminals, have somebody start the engine.  With the engine running at idle, you should be getting approximately 13.1 – 13.9 volts.
  3. With the engine running, have someone rev the engine.  With the increased RPM‘s, you should be getting greater than 14 volts.

If the battery voltage dropped at all during steps 2 or 3, that is an indicator that the alternator is not charging the battery and it should be replaced.

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  • Sharon

    Great tip! You have had to replace my alternator before…

  • Great article. I used to have this problem frequently.

  • Steph

    Great tips!

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  • Helen

    My 2001yukon have had 2 jumps in 24hrsn I called AAA and had them test my battery they said my battery is good and my alternator and starter is good. What can I do. It starts now but I don’t know what’s going on